+1 weapons add 1 to attack rolls and damage rolls made with the weapon. Improved Pact Weapon, similarly, states: "the weapon gains a +1 bonus to its attack and damage rolls". What needs to be determined, then, is whether or not your spell attacks are made or at least can be made 'with' your weapon. That's largely a matter of how spellcasting works in your setting.
It should be noted that the item's role as an Arcane Focus should not in-itself allow the bonus to apply to spells. While that is the plainest reading of the text, 5e is not meant to be played according to its rules text as a corpus but rather with each part of the text somehow existing in isolation. Since that reading involves using two areas of the rules at once, then, and since the rules do not specially call out that doing so will work okay, it is highly suspect, moreso because that would be a departure from the function of such weapons in previous versions of the game, and that usually warrants clear text on the part of the authors.
So, basically, if you can't add the bonus to a spell attack that means that you can't actually meaningfully incorporate your pact weapon into said spell, and if you can then you are making the attack with the weapon, in some sense.